1. Field of the Invention
The present invention relates to a data output circuit.
2. Description of the Related Art
An electronic device such as a car stereo having a liquid crystal display panel is equipped with a data processing system for processing data or signals from an operation unit such as a key pad, an infrared remote control, and a rotary encoder switch. Since the data processing at the data processing system is mainly carried out by a microcomputer, it is necessary to input the data from the operating unit into the microcomputer.
FIG. 5 shows an example of a block diagram of a data processing system at a liquid crystal display unit of a car stereo. Infrared data from the infrared remote control, a rotary encoder switch signal A and a rotary encoder switch signal B from a rotary encoder switch (hereinafter, a rotary encoder switch signal will be referred to as a switch signal) are each input directly into a microcomputer 600. On the other hand, a key input resulting from the operation of a key pad 601 is input into the microcomputer 600 via a key data output circuit 610 in a liquid crystal display driver IC (Integrated Circuit) 602 (see, for example, Japanese patent application Laid-Open Publication No. 2004-146806). The microcomputer 600, based on a signal input thereinto, outputs a DI signal into the liquid crystal display driver IC 602. Then, the liquid crystal display driver IC 602 receives the DI signal to output an electrode drive signal for driving an electrode of the liquid crystal display panel. Here, with reference to the timing chart shown in FIG. 6, the key data corresponding to the key input from the key pad 601 will be further described. The key data obtained by operating the key pad 601 is stored in the key data output circuit 610 in the liquid crystal display driver IC 602. When the DI signal as the address of the liquid crystal display driver IC 602 and a high level (H level) CE signal indicating the output of the key data stored in the key data output circuit 610 are input from the microcomputer 600 into the liquid crystal display driver IC 602, the key data is output into the microcomputer 600 as output data DO on the basis of a clock signal CL, as shown in the timing chart of FIG. 6.
In the case of the liquid crystal display unit of a car stereo as mentioned above, it is necessary to input into the liquid crystal display driver IC 602 infrared data or switch signals that were input directly into the microcomputer 600, and to serially output the infrared data or switch signals by using an output signal line 700 that the key data is output into, for the purpose of reducing the number of signal lines leading into the microcomputer.
Moreover, due to the issues of the data processing on the microcomputer side, even if infrared data or switch signals are input into the liquid crystal display driver IC 602, it is required that the timing for starting the output of data coincides with the timing for starting the output of the key data shown in FIG. 6. In the case where the liquid crystal display driver IC 602 serially outputs newly added infrared data or switch signals, however, there is needed a time period for parallel-to-serial converting, which disadvantageously results in the problem that the output of data cannot be started at the same timing as that for the output of the key data to be started shown in FIG. 6.